1. Field of the Invention
The present invention relates to a drive system for driving an objective lens and an optical pickup apparatus.
2. Description of the Related Art
FIGS. 5A to 5C are views each showing an actuator 40 according to a first related art. FIG. 5A is a top view, FIG. 5B a side view, and FIG. 5C a sectional view taken along cross-section line D-D shown in FIG. 5A. The actuator 40 is adapted to an optical pickup apparatus where an optical disk is used as a recording medium. In order to record or reproduce information on the optical disk 11, the actuator 40 includes a focus direction drive unit which controls a light beam 12 collected by an objective lens 401 to focus at an optimum position on the optical disk 11, a tracking direction drive unit which follows a specific track, and a tilt direction drive unit which optionally tilts the objective lens 401 in accordance with a tilt of the optical disk 11.
In the focus direction drive section a lens holder 402 holding the objective lens 401 is driven in an optical axis direction by means of a drive mechanism with a focus coil 408 and a magnet 405 so that a beam spot is focused on the optical disk 11. In the tracking direction drive unit, the lens holder 402 holding the objective lens 401 is driven in a radial direction of an optical disk 11 orthogonal to the optical axis direction by means of a drive mechanism with a tracking coil 407 and a magnet 404 so that the beam spot follows the specific track on the optical disk 11.
In the tilt direction drive unit, the lens holder 402 holding the objective lens 401 is tilted in accordance with the tilt of the optical disk 11 by means of a drive mechanism with a tilt coil 406 and a magnet 410. The lens holder 402 holds not only the objective lens 401 but also the focus coil 408, the tracking coil 407, and the tilt coil 406 integrally.
A support member 413 fixed to a base plate 403 supports the lens holder 402 with the aid of six elastic support members 409, for example, which are arranged in parallel to each other, like vertically-arranged three by laterally-arranged two. The elastic support members 409 are deformed to be curved by drive force of the focus coil 408, the tracking coil 407, the tilt coil 406, the magnet 404, the magnet 405, and the magnet 410, thereby allowing for movement in the focus direction, tracking direction, and tilt direction.
In an objective lens drive according to a second related art, tilt coils are disposed on opposite sides in a tracking direction, of a displaceable lens holder, and at a position outside each of the tilt coils is disposed a tilt magnet which is vertically divided into two magnet parts with different polarities (refer to Japanese Unexamined Patent Publication JP-A 2003-115124).
In an optical head device according to a third related art, it is not necessary to provide the magnet for driving only a tilt coil, but tracking coils are disposed on opposite sides in a tracking direction, of a focus coil displaceable. Furthermore, two tilt coils are laterally arranged in the tracking direction under the focus coil, and the moment generated by the respective tilt coils allows for movement driven in a tilt direction (refer to Japanese Unexamined Patent Publication JP-A 2003-173556).
In an objective lens drive according to a fourth related art, two focus coils are disposed laterally with a distance therebetween, and so are two magnets (refer to Japanese Unexamined Patent Publication JP-A 11-312327).
In the first and second related art, the magnet only used for the tilt coil is provided, therefore entailing a problem that the actuator is increased in size to secure a space required for the magnet, which causes an increase in cost, even if the magnet is not divided into the magnet parts with different polarities. Furthermore, in the second related art, the drive force may be unstable depending on a displaceable position in the tracking direction.
In the third related art, the tracking coils are disposed on the opposite sides in the tracking direction, of the focus coil displaceable, and in order to secure displacement in the tracking direction, a problem arises that a magnet is inevitably large in width. Furthermore, in such a configuration that the two tilt coils are laterally arranged in the tracking direction under the focus coil and that the moment generated by the respective tilt coils allows for movement driven in the tilt direction, it is hard to generate the drive force with small electricity due to the arrangement remote from a position of center of gravity of the lens holder.
In the fourth related art having two laterally-separated focus coils and two laterally-separated magnets, the displacement in the tracking direction needs to be secured while the two magnets are distanced as far away as possible from each other, in order to promote the generation of the drive force in the tilt direction. Furthermore, in order to use the divided magnet to obtain the drive force in the focus direction, the magnet needs to have its width secured and therefore causes a problem of size increase in the tracking direction of the apparatus.